When articles such as metal parts are formed, it is sometimes desirable to harden the parts to improve durability and wear characteristics. One way to harden the part is to immerse the part in a quench system immediately after heating the part to the desired heat treat temperature. Many different types of media can be used in the quench system, including oil or water, or aqueous polymer solutions, depending on a variety of factors including the material from which the part is made and the desired hardness and microstructural characteristics of the part.
It is desirable for the quench system to provide uniform cooling and for the cooling to be repeatable. Nonuniform cooling can result in varying degrees of hardness, quench cracks, increased distortion and other problems. There are many factors that contribute to nonuniformity of cooling within the quench system. These may include the tank shape and depth, flow rates within the system and impurities in the system fluid.
Typically, to determine the effectiveness or cooling power of a particular quench system, it has been necessary to quench one or more parts or samples in various areas of the quench system, then cut these parts through one and sometimes several sections to thoroughly analyze hardness and microstructure. However, this procedure is extremely labor intensive and destroys what might otherwise have been a usable part. Moreover, the test only determines the effectiveness at one point in time. It cannot actively monitor the effectiveness of a quench system.
There is one type of quench cooling effectiveness apparatus known in the prior art. That type of apparatus is generally disclosed in U.S. Pat. No. 4,563,097 (hereinafter referred to as "the '097 patent"), entitled "Method of Evaluating Cooling Performance of Heat Treatment Agent And Apparatus Therefor". The '097 patent discloses an apparatus having a single resistance temperature detector ("RTD"). This apparatus applies varying current levels to the RTD which causes the RTD to be heated to different temperature levels. Because a temperature/resistance relationship is known for the RTD, the apparatus can determine the RTD temperature as a function of the voltage applied to the RTD and a measured current through the RTD.
In the '097 patent, the RTD sensor is installed into a quench system and the RTD temperature is varied to produce a dissipated heat v. temperature curve for that particular quench media. The effectiveness of different quench media can thereby be analyzed. For example, one particular quench medium may dissipate heat most effectively for parts cooling to 650 degrees Centigrade while another fluid may be more effective on parts cooling to 550 degrees Centigrade. From the curves produced for the various quench media, the most effective fluid can be selected and utilized for a particular part.
However, an apparatus such as that disclosed in the '097 patent suffers from several disadvantages. For example, the sensor itself is repeatedly heated to relatively hot temperatures to simulate the temperature of the parts to be quenched. The repeated heating and cooling of the sensor causes the sensor to have a short life span and the sensors often fail. Another disadvantage of the disclosed apparatus is that it generally must be installed through a wall of the quench tank. Moreover, the apparatus cannot be quickly moved within the tank to determine effectiveness of different positions in the tank. The apparatus also does not simulate the shape of a typical part to be quenched. Thus, cooling characteristics of the apparatus may be significantly different from those of an actual part. Fluid flow in the quench system can differ significantly once actual parts are placed in the system, and since the apparatus isn't portable, it can't easily be placed between parts to determine this effect. For at least these reasons, the quench cooling effectiveness apparatus disclosed in the '097 patent may not be a good predictor of actual quench characteristics experienced by actual parts.
The present invention is directed toward overcoming one or more of the disadvantages associated with the prior art quench cooling effectiveness apparatus.